In schooling, the teachers usually give explanation to students with blackboard, i.e., a teacher would write what is to teach on a blackboard during the class hours. Since the available space of a blackboard is limited for the unlimited subject matters, the teacher has to repeatedly erase the subjects on the blackboard already explained so as to give space to the next subject. After each erasing, a large quantity of chalk powder will be left on the eraser; then, the eraser has to be cleaned; otherwise, the eraser would be unable to erase the blackboard efficiently, and a large quantity of chalk powder would fall and fly in the air after each erasing motion. The flying chalk powder would jeopardize a person's lungs (It is reported that teachers would have over ten times of possibility to suffer from pulmonary emphysema than other people). Moreover, whenever a large amount of flying chalk powder falls on one's face, hairs and hands, it would be rather diffecult to clean, and it would cause a had appearance to a person. In order to avaid such a case, the teacher has to remove the powder on the eraser repeatedly. When the teacher cleans an eraser, it would also cause the powder to fly in the air. This chalk powder problem has annoyed the teachers for many years; this problem has recently been improved by means of a chalk-powder cleaning machine; unfortunately, that machine has to be operated with electric power, and that requirement causes another inconvenient drawback during practical use in classroom; therefore, the present invention is developed to improve the aforesaid drawback.